The invention is directed to a drilling machine, in particular a core drilling machine, comprising a stand, whereon a carriage is guided, the carriage being movable along a guide by means of a drive in a working direction, wherein on the carriage a drilling unit is supported that comprises a spindle being driven by a motor for driving a drilling tool.
From German patent application DE 4 019 515 A1 a magnetic stand drilling unit is known which comprises a frame and a magnetic stand which attaches magnetically to a drilling work piece, further comprising an electric drilling machine having a motor and a feed motor designed as a DC motor being supported on the frame for feeding the drill toward the work piece and for returning there from, wherein a control is provided comprising a sensing means for sensing the completion of a bore drilling operation on the work piece, further comprising feed reversing motor means for reversing the motion direction of the feed motor, as well as safety switching means for deactivating the drilling motor and the feed motor when sensing an overload state.
By using such a control an overload state can be avoided, however the design is relatively costly and complicated.
In a drilling machine known from German patent application DE 3 708 038 A1 a drilling head is provided, a drive motor coupled with the drilling head for driving operation, a power supply means for supplying power to the drive motor, and a feed motor being designed as a series motor for displacing the drilling head relatively to the work piece.
Again, for avoiding an overload state a control means is provided having a sensing means for sensing the current fed to the drive motor, a storage means for storing a current level which is sensed when the drilling head is not engaged with the work piece, and further comprising a sensing means for determining, whether a drilling operation is completed or not, depending on an actual current level and the stored current level.
Also the design of this drilling machine is relatively costly and complicated.